A 20-Foot Sea Wall Won’t Save Miami – But Living Structures Can

Yves here. I know some of you will react, “But why should we save Miami?” Since a lot of people would say that about Manhattan, please just treat Miami as a case study.

By Landolf Rhode-Barbarigos, Assistant Professor of Civil, Architectural and Environmental Engineering, University of Miami and Brian Haus, Professor of Ocean Sciences, University of Miami. Originally published at The Conversation

Miami is all about the water and living life outdoors. Walking paths and parks line large stretches of downtown waterfront with a stunning bay view.

This downtown core is where the Army Corps of Engineers plans to build a US$6 billion sea wall, 20 feet high in places, through downtown neighborhoods and right between the Brickell district’s high-rises and the bay.

There’s no question that the city is at increasing risk of flooding as sea level rises and storms intensify with climate change. A hurricane as powerful as 1992’s Andrew or 2017’s Irma making a direct hit on Miami would devastate the city.

But the sea wall the Army Corps is proposing – protecting only 6 miles of downtown and the financial district from a storm surge – can’t save Miami and Dade County. Most of the city will be outside the wall, unprotected; the wall will still trap water inside; and the Corps hasn’t closely studied what the construction of a high sea wall would do to water quality. At the same time, it would block the water views that the city’s economy thrives on.

Much of Miami is built right up to the water’s edge. On average, it’s 6 feet above sea level. Ryan Parker/Unsplash, CC BY-ND

To protect more of the region without losing Miami’s vibrant character, there are ways to pair the strength of less obtrusive hardened infrastructure with nature-based “green” solutions. With our colleagues at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science and the College of Engineering, we have been designing and testing innovative hybrid solutions.

Natural Storm Management

Living with water today doesn’t look the same as it did 50 years ago, or even 20 years ago. Parts of Miami now regularly see “sunny day” flooding during high tides. Salt water infiltrates basements and high-rise parking garages, and tidal flooding is forecast to occur more frequently as sea level rises. When storms come through, the storm surge adds to that already high water.

Hurricanes are less common than tidal flooding, but their destructive potential is greater, and that is what the Army Corps is focused on with its sea wall plan.

If Miami Beach were an undeveloped barrier island, and if thick mangrove forests were still common along the South Florida shoreline, the Miami area would have more natural protection against storm surge and wave action. But most of those living buffers are long gone.

There are still ways nature can help preserve the beauty of Miami’s marine playground, though.

For example, healthy coral reefs break waves, dissipating their energy before the waves reach shore. Dense mangrove forests also dissipate wave energy with their complex root systems that rise above the water line, dramatically reducing the waves’ impact. In areas where coastal flooding is an increasing problem, low-lying communities can be relocated to higher ground and the vacant land turned into wetlands, canals or parks that are designed to manage storm surge flooding.

Coral reefs like these in Biscayne National Park have struggled with warming waters. National Park Service


Each area of coastline is unique and requires different protective measures based on the dynamics of how the water flows in and out. Given Miami’s limited space, living shorelines alone won’t be enough against a major hurricane, but there are powerful ways to pair them with solid “gray” infrastructure that are more successful than either alone.

Hybrid Solutions Mix Green and Gray

Nobody wants to look at a cement breakwater offshore. But if you’re looking at a breakwater covered with corals and hospitable to marine life, and you can go out and swim on it, that’s different.

Corals help the structure dissipate wave energy better, and at the same time they improve water quality, habitat, recreation, tourism and quality of life. For a lot of people, those are some of Miami’s main selling points.

By pairing corals and mangroves with a more sustainable and eco-friendly hard infrastructure, hybrid solutions can be far less obtrusive than a tall sea wall.

For example, a cement-based breakwater structure submerged offshore with coral transplants could provide habitat for entire ecosystems while providing protection. We’re working with the city of Miami Beach through the University of Miami Laboratory for Integrative Knowledge to implement three hybrid coral reefs just offshore that we will monitor for their engineering and ecological performance.

Closer to shore, we’re experimenting with a novel modular marine and estuarine system we call “SEAHIVE.” Below the water line, water flows through hollow hexagonal channels of concrete, losing energy. The top can be filled with soil to grow coastal vegetation such as mangroves, providing even more protection as well as an ecosystem that benefits the bay.

We’re currently working on testing SEAHIVE as a green engineering alternative for North Bay Village, an inhabited island in the bay, and as the infrastructure of a newly developed marine park where these “green-gray” reef and mangrove designs will be showcased.

What About the Rest of Miami?

The Army Corps of Engineers’ draft plan – a final version is expected in the fall – would give nature-based solutions little role beyond a fairly small mangrove and sea grass restoration project to the south. The Corps determined that natural solutions alone would require too much space and wouldn’t be as effective as hard infrastructure in a worst-case scenario.

Instead, the Army Corps’ plan focuses on the 6-mile sea wall, flood gates and elevating or strengthening buildings. It basically protects the downtown infrastructure but leaves everyone else on their own.

Sea walls and flood gates can also affect water flow and harm water quality. The Corps’ own documents warn that the sea walls and gates will affect wildlife and ecosystems, including permanent loss of protective corals, mangroves and sea grass beds.

Mangrove roots rising above the water help break up the energy of waves at the shoreline. Florida Guidebook/Unsplash, CC BY-ND

We would like to see a plan for all of Miami-Dade County that considers the value that green and hybrid solutions bring for marine life, tourism, fishing and general quality of life, in addition to their protective services for the shoreline.

Both types – green and gray – would take time to build out, particularly if the sea wall plan were challenged in court. And both run a risk of failure. Corals can die in a heat wave, and a storm can damage mangroves; but storms can also undermine engineered solutions, like the New Orleans levee system during Hurricane Katrina. To help build resilience, our colleagues at the University of Miami have been breeding corals to be more resistant to climate change, investigating novel cementitious materials and noncorrosive reinforcements and developing new designs for coastal structures.

Miami in the Future

Miami will be different in the coming decades, and the changes are already starting.

High ground is at a premium, and that’s showing up in real estate decisions that are pushing lower-income residents out and into less safe areas. Anybody looking back at Miami will probably think the region should have done a better job of managing growth and maybe even managing some form of retreat from threatened areas.

We don’t want to see Miami become Venice or a city walled off from the water. We think Miami can thrive by making use of the local ecosystem with novel green engineering solutions and an architecture that adapts.

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  1. Synoia

    Mangrove swamps that I recall as a child in Nigeria’s Coast are full of all the rubbish, natural and man made, and end up as nasty cesspits, full of decaying effluent, animals and plant matter. While good for the mangrove plants , this mix it is really unpleasant both in mess and for recreation.

    Those proposing this need to visit existing mangrove swamps and explore their bounty.

    1. freebird

      Yes, they don’t provide a pretty or beachy shoreline. But they do keep the land from eroding and provide very rich habitat for sea life nurseries. They are good for Florida and a reason the Keys don’t wash completely away in storms. But, probably not a realistic solution for Miami.

    2. The Pale Scot

      Along with salt intrusion onto the drinking water, Miami is kaput

      Meant for AEL

    3. Anonymous in Michigan

      A reply to Synoia regardiing Mangrove forests.
      So first, the areas along coastlines where mangroves grow are not ‘swamps’. Secondly, Nigeria has a lot of coastal areas, and I wonder if you could have traversed it all to examine their conditions? Much of Nigeria’s coastal area is more accurately classified as estuaries. These areas that you reference were perhaps near heavily populated areas that suffered, as the natural environment does almost everywhere, from human misuse?

      Thirdly, mangrove forests have an ecological value that has been studied for decades. How long did you engage in your perusal?

      I’ll leave this scientific perusal here.

  2. AEL

    Miami is built on a karst platform. It is riddled with holes in the bedrock. Good luck getting a dyke to keep the water out.

    1. RepubAnon

      That’s it – the sea wall will slow down surge, but the water will simply seep through the porous limestone underneath. It’s like putting a brick wall over a ditch filled with gravel.

    2. Gc54

      Exactly. This has been known for decades. Doesn’t bode well that these engineers missed it. Or perhaps the limited area they plan to circumscribe with concrete barriers is the only part that won’t be infiltrated?

      There’s a nice add on for Google Earth where you set the sea level to see what vanishes. I don’t have the link handy but easy to find. It’s sobering.

  3. The Rev Kev

    Maybe this wall will end up being like the Maginot Line of WW2. That wall was built to keep the German from invading but they never did the bit along the Belgium border. After war broke out, the Germans of course went around the wall itself. Maybe it will be the same with this wall. When it is finished, a storm will push water around the wall and the wall itself will stop the water draining back into the ocean. And as AEL pointed out, those ocean waters will seep through that bedrock like a sponge and fill it up anyway. Just a waste of resources. They may as well invest in forks to push the oceans back.

    1. freebird

      Engineers build stuff on top of the land, which is just an annoying substrate to be dealt with. They do not manage or repair ecological systems. It’s almost like we would need, like, scientists, to plan that.

    2. urblintz

      The A C of E already defaced Florida once, cutting it in half with the cross Florida barge canal. The A C of E destroyed New Orleans.

      The A C of E is discredited.

    3. Mark

      Probably far from it. But also they are engineers. Engineers normally think with a limited tool kit. Even good engineers would still be focussed on the earth/concrete/steel solutions. Ecological solutions fall outside their wheelhouse by a big margin.

      (I’m an engineer.)

  4. Mikkel

    Normally I love these sort of articles (well not just – the real life works behind them), but this one makes me feel like I’m crazy.

    I thought that sea level rise was going to doom Miami because it is built on limestone, meaning that it can’t even be protected by sea walls. I also thought that mangroves won’t help because they will die when submerged and from excess heat… not to mention that coral reefs will almost be functionally extinct by 2050.

    Doing a few minutes of searching, I can see that no, I’m not crazy.

    Putting those links together, I now see that this piece is only focused on the efforts to protect Miami against storm surges – and is completely in denial about the larger problem. Moreover, the Corps’ plan only protects the downtown because that is the only piece of land high enough to “survive” (in the very loosest sense of the word) the century. I don’t believe a regional plan is even possible.

    With this recalibration I don’t feel crazy, just a combination of sadness and pity. We are in the twilight grasping for the last beams of light rather than fully preparing for the inevitable dark.

    As for NYC:

    Klaus Jacob likes to show a similar map, depicting what New York’s coastline might have looked like in the mid-Pliocene epoch, 3 million years ago, the last time the amount of carbon in the atmosphere was around today’s level of 400 parts per million. Sea levels were some 30 meters — or nearly 100 feet — higher. “I am a little bit of an oddball,” he admits, “because I’m saying, ‘Hey, now that we have those forecasts, guys, what are we doing about it?’ ” In panel discussions, he takes self-evident pleasure in playing the prickly contrarian, dismissing popular measures like building dunes or cultivating oyster beds to create natural buffer zones against storms. “Oyster beds are great if you are using them in your kitchen”

    1. Susan the other

      Only Miami proper can be salvaged because it is on higher ground? Whistling past the graveyard.

    2. Milton

      It doesn’t matter because it’s game over anyways but, atmosperic carbon is not staying at 400ppm (actually, around 420 now) but will instead be over 500 in about 20 years. It’s funny because it is so tragic how the elites are just grasping at whatever straws that remain in their hopes to maintain some semblence of a functioning biosphere.

  5. Brooklin Bridge

    First I think the ACOE is spot on as far as the targeted area for it’s wall goes, but I think the wall material should be des barreaux de prison (shhh) instead of solid walls. A sort of grand justice covenant where God supplies the corrective floods as long as we provide containment of the best kind of inhabitants -top draw no less- that will result in the fullest cleansing effect.

  6. Rod

    “Knowing when to hold ‘em and when to fold ‘em” comes to my mind.
    Like most coastal megalopolis’s survivability, solutions must be multifaceted with withdrawal (with accompanying Lo$$e$) acknowledged foremost.
    Extinction Rebellion stresses “Telling The Truth” as an essential first step in addressing the climate crises.
    6 Billion worth of porous sea wall obfuscates that—as does “developing” heat stress resistant corals—imo.

  7. MarkLouis

    I’ll take climate change seriously when our elites (of all political persuasions) stop investing heavily in waterfront real estate.

    1. Robert Hahl

      At that point there will be government bailouts for whoever happens to own the debt and the insurance policies. You, on the other hand, will be underwater.

    2. Basil Pesto

      not entirely sure that the judgement of real-estate investors as a class is a worthy barometer of, well, anything.

    3. eg

      Congratulations — you will enjoy the same fate as the Easter Islanders who dismissed the dangers of deforestation as long as their elites continued to “invest” in Moai …

    4. drumlin woodchuckles

      If you think the elites have a more truth-based view of the future as revealed in where they live, you might want to consider investing in where they live or even moving to where they live, if you can afford to do so.

  8. freebird

    I like the idea of encouraging reefs to develop offshore, and we know that sunken ships and rigs can indeed become viable artificial sort-of reefs.

    But, it’s not that simple to get a major shelf-scale reef to take hold enough to protect the whole coast. If it were a spot suited for this, why is there not a reef there now? Answer, probably problems with current or water clarity or temp or depth etc. The Keys do host reefs, although in sad shape, now coming further north where do we hit the limit of viability for the corals?

    And it seems like we’ve run out of time to get this process going already, never mind waiting for the results of pilot projects and research attempts. Maybe if we’d listened to the warning in 1965…..

    1. Jeremy Grimm

      The US Navy could show the value of their giant aircraft carriers. Several aircraft carriers loaded with ballast — F-35s? — to lower them in the water, double or triple anchored, and chained together might make a workable storm break and contribute to the National Defense by defending a US city from the anger of the Ocean. One big advantage — the storm break would be movable. Also, a line of friendly aircraft carriers would be a scenic reminder of our MIC and all it provides to us.

    1. doug

      ‘No’ usually only postpones until the next filing period.
      Nothing is or will be permanently protected.
      Conservation while still worth every effort is only a delaying tactic.

  9. Michael Hudson

    What about the canals in Miami and Fort Lauderdale — for all the boats to get to and from the ocean? If they go boating, won’t they need “locks” like the Panama Canal to prevent a waterfall gushing in from the Atlantic when they’re opened?
    And New York doesn’t have canals, but it DOES have Canal Street, long below water level — while the West Village was long a swamp into the 18th century.
    Then there’s the underground subway, whose switches were corroded by Hurricane Sandy and still haven’t been fixed out here in Queens.

  10. juno mas

    Yes, the critical thinking of the Commentariat at work!

    These ACOE projects and even “green” engineering attempts are likely to fail with *rapidly* rising ocean levels. Beach replenishment (sand) is a ACOE staple, mostly on the East Coast, and repeatedly fails to stem the tide—especially with rising sea levels. Here’s a link that briefly discusses who pays and the result:

    Sea walls simply defract the energy of storm surges. That energy goes somewhere; usually increasing erosive forces that undermine the sea wall itself. The issue with “green” engineering is that it assumes an understanding of natural system response to changed condiitons (rising sea level). As some commenters point out mangroves are sustained by consistent water levels that allow oxygen transport into the tree through the above water “knees” (which are roots). Submerge the “knees” and the mangrove dies.

    I’ve discussed these sorts attempts to mitigate sea level rise along the California coast with the pre-eminent coastal geomorphologist of our time (Gary Griggs– Professor, UC Santa Cruz) and his studied conclusion is planned retreat. The energy of a rising ocean is not to be contained.

    1. Jeremy Grimm

      One benefit of a sea wall for Miami whether gray or a hybrid-innovative green — its quick failure might demonstrate the futility of similar efforts elsewhere.

  11. Starry Gordon

    To me the more interesting question is the mechanics of how the ACOE was gotten to participate in a major real estate scam. Who made the payoffs, who got them, and of what did they consist? How was the deal effectuated?

  12. a fax machine

    Relevant infrastructure needs:

    – raised railroad tracks (already done in parts of Miami through FEC’s new station, doable elsewhere by filling streets in as Sacramento did in the last century)
    – minneapolis-style skyway (would integrate well with existing Sunrail, Metrorail & peoplemover services)
    – consummately raised water, sewer and power lines
    – new canals, when necessary. These would serve as both storm drains and transportation corridors
    – more boats, boat licensing, ferries and marine rescue/interdiction
    – more helicopters, perhaps even a municipal heliport on top of a car garage

    However, this won’t happen because it would require people to get out of their cars. Most of Florida is not capable of that, and unwilling to consider mass transit use period. Meanwhile, the existing marine industry won’t get anywhere if coastal spaces are used as recreational zones and not municipal docks. Nobody wants to turn a friendly suburban beach or trendy commercial waterfront boulevard into semi truck parking. Perhaps restricting truck sizes (and hours of operation) would alleviate the problem. But again, this requires significantly more intellectual effort than the existing car-dominant structure. A relatively conservative state like Florida will never consider it. Ultimately, the offshore reefs are worth less than individual homeowners’ convenience, which is the ability to drive to work when they want and the ability to have a store or office wherever they want without regard to the larger geography (something which big highway trucks enable).

  13. LPG

    I think the folks commenting here are being incredibly generous to the Army Corps of Engineers. They aren’t stupid and they realize that this is ultimately a fool’s errand. The Corps has long been an extension of capital’s interests — real or imagined (as in their century-long effort to create profitable barge traffic on the upper Mississippi) — and are almost certainly using public money to shore up downtown Miami’s real estate market for as long as possible.

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